Shallow structure of Deception Island, Antarctica, from correlations of ambient seismic noise on a set of dense seismic arrays

P>We investigated the shallow velocity structure of Deception Island volcano, Antarctica, using correlations of ambient seismic noise. We selected long records of noise obtained by eight seismic arrays deployed along the inner coast of Deception during the period 2003-2005. Using these data, we calculated average dispersion curves and estimated local 1-D velocity models for the array sites. The combination of these profiles allowed us to obtain a comprehensive model of the shallow velocity structure of the island. The volcano is composed of relatively soft layers of pyroclastic deposits and sediments extending to a depth of about 400 m, with different degrees of compaction. Two layers with thicknesses of about 100 and 300 m and S-wave velocities of around 0.2-0.8 and 0.7-1.1 km s-1, respectively, can be differentiated. The deeper structure is highly variable in terms of wave velocities and layer depths. Although the resolving capabilities are reduced for these layers, the larger S-wave velocities in the range 1.3-2.8 km s-1 indicate that they can be associated with pre-caldera structures and products. There are substantial differences between the different models, which can be spatially related to heterogeneities in the volcano structure. The lowest S-wave velocities may be related to the alterations produced by hydrothermal activity near the surface. On the contrary, the largest velocities occur near the caldera border, revealing the presence of compact materials at shallow depths. Sharp lateral variations can also be observed in the northwest of the bay, which points to the presence of NW-SE faults and/or strong velocity gradients.